In current vehicles, seat belts or safety belts are an indispensable means guaranteeing the safety of the occupant. It is in this case it is very common to check by means of a pressure switch, which is provided in a belt buckle and intended to secure the seat belt, whether the seat belt is properly applied as intended, or locked in. However, this mechanism is easily circumvented, for example with blind belt buckles, or with locking tongues, but also with improper guiding or progression of the seat belt—for example behind a vehicle seat. This not only makes it possible to easily undermine legal regulation, but it also endangers the safety of the vehicle occupants.
From CN 204196844 U is known a warning device by means of which a correct carrying or placement of the seat belt as well as corresponding bypassing attempts are detected and a warning is to be generated when required.
For this purpose, sensors are used which are arranged in a belt buckle for detecting a vertical and a horizontal component of a tension or force acting on the belt buckle and which are compared to predetermined values.
The document DE 10 2010 023 491 A1 discloses a buckle application detecting device for a seat belt whose purpose is to detect with reliability whether an occupant of a vehicle has buckled up a seat belt. For this purpose, the closed state of a belt buckle, the extraction of a belt buckle or the length of the extension of the seat belt can be detected by respective sensors, and also the tightening of the force that is applied to tighten a seat belt can be detected. With a corresponding evaluation and comparison to typical values or reference values, it can then be inferred whether the occupant is buckled in as intended.
The document U.S. Pat. No. 6,767,031 B2 discloses a device and a method for controlling a seat belt wherein the wearing status of the seat belt is detected by a corresponding sensor and the belt is motorized so that it can be rolled up and unrolled. In addition, one sensor is provided for determining the tension or the tensile force of the belt. This is compared to a specified value in order to determine whether the belt is being worn by the passenger.